The goal of this proposal is to determine the role of small non-coding microRNAs (miRNA) in pancreatic islet development. We hypothesize that miRNA regulate the expression of genes controlling islet development. Although miRNA are known to influence the development of several tissues, and they have been implicated in glucose-stimulated insulin secretion in mature beta-cells, the role of miRNA in pancreatic development has not been explored previously. The specific aims of this proposal are to establish the global role of miRNA in pancreas and islet development and to understand the role of individual miRNA: 1. Test the importance of miRNA in pancreas development by removing either Dicer or DGCR8, two components of the pathway for processing miRNA, from early pancreatic precursor cells with pdx1-cre, early islet precursor cells with ngn3-cre, and mature beta-cells with ins2-cre. 2. Determine the expression pattern of miRNAs during pancreas development. We will use miRNA oligonucleotide microarrays that we have already developed and tested, in situ hybridization, and BAG transgenics to determine the expression pattern of miRNAs during pancreatic development. 3. Test the role of specific miRNA in regulating expression of pancreatic transcription factors. Based on predicted miRNA targets, we will focus on the regulation of homeodomain factor Nkx6.1. 4. Establish the mechanisms for regulation of miRNA expression in the pancreas. We will test specifically for regulation of miRNA by pancreatic transcription factors Sox9, Neurogenin3 and Nkx2.2. These studies will help us understand how islet cells differentiate and the role of miRNA in that process. A better understanding of how islet cells differentiate will help in developing methods for producing islet cells for patients with diabetes.